vertebrate

[vur-tuh-brit, -breyt]

vertebrate, any animal having a backbone or spinal column. Verbrates can be traced back to the Silurian period. In the adults of nearly all forms the backbone consists of a series of vertebrae. All vertebrates belong to the subphylum Vertebrata of the phylum Chordata. There are five classes of vertebrates: fish, amphibians, reptiles, birds, and mammals. General characteristics of vertebrate animals include their comparatively large size, the high degree of specialization of parts they exhibit, their bilaterally symmetrical structure, and their wide distribution over the earth. In addition to an internal skeleton of bone and cartilage or of cartilage alone, vertebrates have a spinal cord, a brain enclosed in a cranium, a closed circulatory system, and a heart divided into two, three, or four chambers. Most have two pairs of appendages that are variously modified as fins, limbs, or wings in the different classes. All animals without backbones are called invertebrates; these do not form a homogeneous group as do vertebrates.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

vertebrate

Any animal of the chordate subphylum Vertebrata, which includes the fishes, amphibians, reptiles, birds, and mammals. Vertebrates have an internal skeleton formed of cartilage, bone, or both. The skeleton consists of a backbone (vertebral column), which partly encloses a spinal cord; a skull, which encloses the brain; and usually two pairs of limbs. Nerves extending from the spinal cord and brain permeate the skin, muscles, and internal organs. The muscular system consists primarily of bilaterally paired masses attached to bones or cartilage. Skin and scales, feathers, fur, or hair cover the outer surface. Seealso invertebrate.

Learn more about vertebrate with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Vertebrate

Vertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae. For this reason, the sub-phylum is sometimes referred to as "Craniata", as all members do possess a cranium. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony fish, sharks and rays, amphibians, reptiles, mammals, and birds. Extant vertebrates range in size from the carp species Paedocypris, at as little as 7.9 mm (0.3 inch), to the Blue Whale, at up to 33 m (110 ft).

Anatomy and morphology

One characteristic of the subphylum are that all members have muscular systems that mostly consist of paired masses, as well as a central nervous system which is partly located inside the backbone (if one is present). The defining characteristic of a vertebrate is considered the backbone or spinal cord, a brain case, and an internal skeleton, but the latter do not hold true for lampreys, and the former is arguably present in some other chordates. Rather, all vertebrates are most easily distinguished from all other chordates by having a clearly identifiable head, that is, sensory organs – especially eyes are concentrated at the fore end of the body and there is pronounced cephalization. Compare the lancelets which have a mouth but not a well-developed head, and have light-sensitive areas along their entire back.

Evolutionary history

Vertebrates originated about 500 million years ago during the Cambrian explosion, which is part of the Cambrian period. The earliest known vertebrate is Myllokunmingia. According to recent molecular analysis Myxini (hagfish) also belong to Vertebrates. Others consider them a sister group of Vertebrates in the common taxon of Craniata.

Fossil record

The earliest known fossil records of vertebrates are Myllokunmingia fengjiaoa and Haikouichthys ercaicunensis, dating somewhere between 513–542 mya during the Early Cambrian. The fossils were discovered in Yunnan, China

Taxonomy and classification

Classification after Janvier (1981, 1997), Shu et al. (2003), and Benton (2004).

Subphylum Vertebrata

(Unranked group) Hyperoartia (lampreys)
Class †Conodonta
Subclass †Pteraspidomorphi
Class †Thelodonti
Class †Anaspida
Class †Galeaspida
Class †Pituriaspida
Class †Osteostraci
Infraphylum Gnathostomata (jawed vertebrates)

* Class †Placodermi (Paleozoic armoured forms)

* Class Chondrichthyes (cartilaginous fish)

* Class †Acanthodii (Paleozoic "spiny sharks")

* Superclass Osteichthyes (bony fish)

* Class Actinopterygii (ray-finned fish)

* Class Sarcopterygii (lobe-finned fish)

* Subclass Coelacanthimorpha (coelacanths)

* Subclass Dipnoi (lungfish)

* Subclass Tetrapodomorpha (ancestral to tetrapods)

* Superclass Tetrapoda (four-limbed vertebrates)

* Class Amphibia (amphibians)

* Series Amniota (amniotic embryo)

* Class Sauropsida (reptiles and birds)

* Class Aves (birds)

* Class Synapsida (mammal-like reptiles)

* Class Mammalia (mammals)

Etymology

The word vertebrate derives from Latin vertebrātus (Pliny), meaning having joints. It is closely related to the word vertebra, which refers to any of the bones or segments of the spinal column.